An antenna may be constructed from a plurality of radiating elements arranged into a series of vertical radiating columns. In such an arrangement, the relative spacing of the columns determines the beamwidth of the antenna. The arrangement of the antenna will also typically dictate the direction of the center of the beam, i.e., the azimuth scan angle. In certain applications, it may be desirable to change the beamwidth and/or azimuth scan angle of an antenna.
One approach to changing the beamwidth of an antenna is to physically change the relative spacing of the columns, or to exchange or swap the antenna for another antenna having a different column spacing. Similarly, the azimuth scan angle may be, changed by adjusting the physical arrangement of the antenna. Typical of cellular and other communication applications, an antenna is placed atop a tower, a building or in other locations where physical access is limited. Changing the beamwidth or azimuth scan angle in such cases can be costly and difficult. Moreover, such physical handling of the antenna may require that service be interrupted during the handling process.
Other approaches for changing the beamwidth of an antenna involve variation of the phase of the electrical signal applied to the radiating columns. A relatively low cost and simple approach is to provide a series of ganged mechanical phase shifters which are varied in unison to affect the phase of the signal to the radiating columns, and hence, the beamwidth of the antenna. Such ganged mechanical phase shifters have the advantage of simplifying the beamwidth change, but are of limited utility. An approach which may have greater utility than the ganged mechanical phase shifters is a fully adaptive array or smart antenna. Smart antennas utilize electronic networks which present other drawbacks, however, including the fact that they are very complex and costly, and perhaps prohibitively so.
There is a need to provide a variable beamwidth and/or variable azimuth scan angle antenna that relies on the principle of phase shifters to adjust the beamwidth and/or azimuth scan angle with the advantages of both the ganged mechanical phase shifters and the smart antenna, but without their respective drawbacks.